??? Index exceeds matrix dimensions.

I keep getting this error every time I run this code. Can you tell me where I am wrong? I have run through the debugger and can't seem to figure out where I went wrong.

K = zeros(3*NN,3*NN);
M = zeros(3*NN,3*NN);
for n = 1:NE
    i = Dir(n,2);
    j = Dir(n,3);
    K(3*i-2:3*i,3*i-2:3*i)= K11(:,:,n) + K(3*i-2:3*i,3*i-2:3*i);
    K(3*i-2:3*i,3*j-2:3*j)= K12(:,:,n);
    K(3*j-2:3*j,3*i-2:3*i)= K21(:,:,n);
    K(3*j-2:3*j,3*j-2:3*j)= K22(:,:,n) + K(3*j-2:3*j,3*j-2:3*j);

      M(3*i-2:3*i,3*i-2:3*i)= M11(:,:,n) + M(3*i-2:3*i,3*i-2:3*i);
      M(3*i-2:3*i,3*j-2:3*j)= M12(:,:,n);
      M(3*j-2:3*j,3*i-2:3*i)= M21(:,:,n);
      M(3*j-2:3*j,3*j-2:3*j)= M22(:,:,n) + M(3*j-2:3*j,3*j-2:3*j);

end

[Azzi Abdelmalek]

what are NN NE Dir,..?

[Walter Roberson]

Azzi is right: the information you have given us does not allow us to determine whether 3*i-2 to 3*i and 3*j-2 to 3*j are within the size of K and M; we also cannot tell that the third dimension of K* and M* are at least as big as NE.

[Jonathan]

Thank you for your suggestions. I am a nubie at Matlab and I'm trying to learn it as fast as I can. In response to your questions, NN and NE are the number of nodes and number of elements respectively.

I will try to post most of the code for you to see what I'm talking about.

NN = xlsread('test','Input','B2');
coord = xlsread('test','Input','A4:C8');
for j = 1:NN
    i = coord(j,1);
    x(i) = coord(j,2);
    y(i) = coord(j,3);
%     plot(x,y)
%     hold on
end

NE = xlsread('test','Input','F2');  
Pro = xlsread('test','Input','E4:K7');
for j = 1:NE
    i = Pro(j,1);
    I(i) = Pro(j,4);
    A(i) = Pro(j,5);
    E(i) = Pro(j,6);
    m_bar(i) = Pro(j,7);
    Dir(i,1) = i;
    Dir(i,2) = Pro(j,2);
    Dir(i,3) = Pro(j,3);
end

NC = xlsread('test','Input','N2');
cons = xlsread('test','Input','M4:O6');

for i = 1:NE
    L(i) = sqrt((x(Dir(i,3))-(x(Dir(i,2))))^2 + (y(Dir(i,3))-(y(Dir(i,2))))^2);
    Cos(i) = ((x(Dir(i,3))-(x(Dir(i,2)))))/L(i);
    Sin(i) = ((y(Dir(i,3))-(y(Dir(i,2)))))/L(i);
end

mass_kind = 0;

for i = 1:NE
    S(i) = (E(i)*A(i))/L(i)^3;
    k11(:,:,i) = S(i)*[A(i)*L(i)^2/I(i) 0 0;0 12 6*L(i);0 6*L(i) 4*L(i)^2];
    k12(:,:,i) = S(i)*[-A(i)*L(i)^2/I(i) 0 0;0 -12 6*L(i);0 -6*L(i) 2*L(i)^2];
    k21(:,:,i) = S(i)*[-A(i)*L(i)^2/I(i) 0 0;0 -12 -6*L(i);0 6*L(i) 2*L(i)^2];
    k22(:,:,i) = S(i)*[A(i)*L(i)^2/I(i) 0 0;0 12 -6*L(i);0 -6*L(i) 4*L(i)^2];

      if mass_kind == 0
          Q(i) = m_bar(i)*L(i)/420;
          m11(:,:,i) = Q(i)*[140 0 0;0 156 22*L(i);0 22*L(i) 4*L(i)^2];
          m12(:,:,i) = Q(i)*[70 0 0;0 54 -13*L(i);0 13*L(i) -3*L(i)^2];
          m21(:,:,i) = Q(i)*[70 0 0;0 54 13*L(i);0 -13*L(i) -3*L(i)^2];
          m22(:,:,i) = Q(i)*[140 0 0;0 156 -22*L(i);0 -22*L(i) 4*L(i)^2];
      else
          Q(i) = m_bar(i)*L(i)/2;
          m11(:,:,i) = Q(i)*eye(3,3); m11(3,3,i) = 0;
          m12(:,:,i) = Q(i)*eye(3,3);
          m21(:,:,i) = Q(i)*eye(3,3);
          m22(:,:,i) = Q(i)*eye(3,3); m22(3,3,i) = 0;
      end
  end

for n = 1:NE
    T(:,:,n) = [Cos(n) Sin(n) 0;-Sin(n) Cos(n) 0;0 0 1];
    for i = 1:3
        for j = 1:3
            Tt(i,j,n) = T(j,i,n);
        end
    end
end

for i = 1:NE
    K11 = Tt(:,:,i)*k11(:,:,i)*T(:,:,i);
    K12 = Tt(:,:,i)*k12(:,:,i)*T(:,:,i);
    K21 = Tt(:,:,i)*k21(:,:,i)*T(:,:,i);
    K22 = Tt(:,:,i)*k22(:,:,i)*T(:,:,i);

      M11 = Tt(:,:,i)*m11(:,:,i)*T(:,:,i);
      M12 = Tt(:,:,i)*m12(:,:,i)*T(:,:,i);
      M21 = Tt(:,:,i)*m21(:,:,i)*T(:,:,i);
      M22 = Tt(:,:,i)*m22(:,:,i)*T(:,:,i);
  end

K = zeros(3*NN,3*NN);
M = zeros(3*NN,3*NN);
for n = 1:NE
    i = Dir(n,2);
    j = Dir(n,3);
    K(3*i-2:3*i,3*i-2:3*i)= K11(:,:,n) + K(3*i-2:3*i,3*i-2:3*i);
    K(3*i-2:3*i,3*j-2:3*j)= K12(:,:,n);
    K(3*j-2:3*j,3*i-2:3*i)= K21(:,:,n);
    K(3*j-2:3*j,3*j-2:3*j)= K22(:,:,n) + K(3*j-2:3*j,3*j-2:3*j);

      M(3*i-2:3*i,3*i-2:3*i)= M11(:,:,n) + M(3*i-2:3*i,3*i-2:3*i);
      M(3*i-2:3*i,3*j-2:3*j)= M12(:,:,n);
      M(3*j-2:3*j,3*i-2:3*i)= M21(:,:,n);
      M(3*j-2:3*j,3*j-2:3*j)= M22(:,:,n) + M(3*j-2:3*j,3*j-2:3*j);

end

Answer 1

[Jan]

Use the debugger again:

dbstop if error

Then start the code. Matlab stops when the error occurs and you can evaluate the parts of the currently processed line in the command window, e.g.:

K11(:, :, n)
K(3*i-2:3*i, 3*i-2:3*i)

Then you will find out, which of the statements cause the error. Btw. the responsible line is shown in the error message also, and therefore it is a good idea to post the complete error messages, if you want help in the forum.

Another hint: If you use temporary variables for the index expressions, the code will look cleaner:

a = 3*i-2;
b = 3*i;
c = 3*j-2;
d = 3*j;

Beside the reduction of runtime, the improved readability will allow for an easier debugging.

[Jonathan]

Thank you for your suggestions. I will try to clean up the code so its easier to read.

[Jonathan]

Here is the cleaned up version of code.

dbstop if error

%input data
NN = xlsread('test','Input','B2');          %Input Number of Nodes
coord = xlsread('test','Input','A4:C8');    %Coordinates
for j = 1:NN
    i = coord(j,1);
    x(i) = coord(j,2);
    y(i) = coord(j,3);
%     plot(x,y)                             %Plots OK
%     hold on
end

NE = xlsread('test','Input','F2');          %Number of Elements
Pro = xlsread('test','Input','E4:K7');      %Properties of Elements
for j = 1:NE
    i = Pro(j,1);
    I(i) = Pro(j,4);
    A(i) = Pro(j,5);
    E(i) = Pro(j,6);
    m_bar(i) = Pro(j,7);
    Dir(i,1) = i;
    Dir(i,2) = Pro(j,2);
    Dir(i,3) = Pro(j,3);
end

NC = xlsread('test','Input','N2');          %Number of Constraints
cons = xlsread('test','Input','M4:O6');     %Constraints

%Length of Elements
for i = 1:NE
    L(i) = sqrt((x(Dir(i,3))-(x(Dir(i,2))))^2 + (y(Dir(i,3))-(y(Dir(i,2))))^2);
    Cos(i) = ((x(Dir(i,3))-(x(Dir(i,2)))))/L(i);
    Sin(i) = ((y(Dir(i,3))-(y(Dir(i,2)))))/L(i);
end

%Insert here for nodal loads
mass_kind = 0;

%Element Stiffness/Mass Matrics
for i = 1:NE
    S(i) = (E(i)*A(i))/L(i)^3;
    k11(:,:,i) = S(i)*[A(i)*L(i)^2/I(i) 0 0;0 12 6*L(i);0 6*L(i) 4*L(i)^2];
    k12(:,:,i) = S(i)*[-A(i)*L(i)^2/I(i) 0 0;0 -12 6*L(i);0 -6*L(i) 2*L(i)^2];
    k21(:,:,i) = S(i)*[-A(i)*L(i)^2/I(i) 0 0;0 -12 -6*L(i);0 6*L(i) 2*L(i)^2];
    k22(:,:,i) = S(i)*[A(i)*L(i)^2/I(i) 0 0;0 12 -6*L(i);0 -6*L(i) 4*L(i)^2];

      if mass_kind == 0
          Q(i) = m_bar(i)*L(i)/420;
          m11(:,:,i) = Q(i)*[140 0 0;0 156 22*L(i);0 22*L(i) 4*L(i)^2];
          m12(:,:,i) = Q(i)*[70 0 0;0 54 -13*L(i);0 13*L(i) -3*L(i)^2];
          m21(:,:,i) = Q(i)*[70 0 0;0 54 13*L(i);0 -13*L(i) -3*L(i)^2];
          m22(:,:,i) = Q(i)*[140 0 0;0 156 -22*L(i);0 -22*L(i) 4*L(i)^2];
      else
          Q(i) = m_bar(i)*L(i)/2;
          m11(:,:,i) = Q(i)*eye(3,3); m11(3,3,i) = 0;
          m12(:,:,i) = Q(i)*eye(3,3);
          m21(:,:,i) = Q(i)*eye(3,3);
          m22(:,:,i) = Q(i)*eye(3,3); m22(3,3,i) = 0;
      end
  end

%Transformation Matrices
for n = 1:NE
    T(:,:,n) = [Cos(n) Sin(n) 0;-Sin(n) Cos(n) 0;0 0 1];
    for i = 1:3
        for j = 1:3
            Tt(i,j,n) = T(j,i,n);
        end
    end
end

%Transformation from Local to Global Coordinates
for i = 1:NE
    K11 = Tt(:,:,i)*k11(:,:,i)*T(:,:,i);
    K12 = Tt(:,:,i)*k12(:,:,i)*T(:,:,i);
    K21 = Tt(:,:,i)*k21(:,:,i)*T(:,:,i);
    K22 = Tt(:,:,i)*k22(:,:,i)*T(:,:,i);

      M11 = Tt(:,:,i)*m11(:,:,i)*T(:,:,i);
      M12 = Tt(:,:,i)*m12(:,:,i)*T(:,:,i);
      M21 = Tt(:,:,i)*m21(:,:,i)*T(:,:,i);
      M22 = Tt(:,:,i)*m22(:,:,i)*T(:,:,i);
  end

%Global/Mass Matrices
K = zeros(3*NN,3*NN);
M = zeros(3*NN,3*NN);
for n = 1:NE
    i = Dir(n,2);
    j = Dir(n,3);
    a = 3*i-2;
    b = 3*i;
    c = 3*j-2;
    d = 3*j;
    K(a:b,a:b)= K11(:,:,n) + K(a:b,a:b);
    K(a:b,c:d)= K12(:,:,n);
    K(c:d,a:b)= K21(:,:,n);
    K(c:d,c:d)= K22(:,:,n) + K(c:d,c:d);

      M(a:b,a:b)= M11(:,:,n) + M(a:b,a:b);
      M(a:b,c:d)= M12(:,:,n);
      M(c:d,a:b)= M21(:,:,n);
      M(c:d,c:d)= M22(:,:,n) + M(c:d,c:d);

end

[Jonathan]

The error message as shown in the command window. I appreciate your help with this program.

??? Index exceeds matrix dimensions.

Error in ==> main3 at 100
    K(a:b,a:b)= K11(:,:,n) + K(a:b,a:b);